$1m reward in Sydney gay hate attack case

The family of Scott Johnson who was killed in a suspected anti-gay hate crime hope a new $1 million reward will bring his killers to justice and will spark a bigger probe into other unsolved gay hate attacks.

Mr Johnson, an American mathematician who was based in Sydney, was discovered at the base of a cliff below a gay beat near Manly's North Head in December 1988.

His death was initially ruled to be a suicide but coroner Michael Barnes last year found the 27-year-old fell from the cliff "as a result of actual or threatened violence" by people who attacked him over his sexuality.

The coroner, who criticised the initial police investigation as inadequate, found it likely more than one person set upon the "young and strong and fit" Mr Johnson while he was at the known gay beat.

Police on Sunday were joined by Mr Johnson's brother Steve to announce a $1 million reward for information leading to the conviction of those responsible for the death.

It comes after the case was referred to a specialist team that is conducting fresh inquiries.

Speaking on the anniversary of his brother's death, Steve Johnson told reporters it was a solemn day but his family was hopeful of finally getting answers.

"Unfortunately, like many other gay men in the 1980s he got tragically unlucky," he told reporters in Sydney on Sunday.

"We're with you now, we're going to find out what happened, we may finally get answers and justice for you."

He also hopes the investigation will mark the beginning of a more thorough probe into the unsolved cases of anti-gay hate crime from the 1970s.

NSW Police Commissioner Mick Fuller said there would be people who are "embarrassed" because they were part of such "terrible" criminal acts in the past.

"It's horrendous to believe that these people are still out in our community - existing, living, free, while Scott ... has died a terrible death," he said on Sunday.

Mr Fuller appealed for anyone with information to come forward.

"If you're out there, if you know something, if you know who committed this crime, if you know who was at the scene at the time, there is a million dollars on the table to get to the bottom of the truth."